Rolling bearings such as angular ball bearings are used for support of shafts which rotate at relatively high speed such as various types of spindles used on working tools. As lubricating methods for lubricating rolling bearings for supporting such spindles which rotate at high speed, conventionally, an oil-air lubricating method has mainly been used in many cases.
The oil-air lubricating method is a method for blowing a minute amount of lubricating oil which is intermittently supplied towards the rolling bearing through piping by virtue of compressed air, and in this method, since the lubricating oil is supplied to the bearing by being caused to forcibly pass through an air curtain formed around the rolling bearing which rotates at highs speed, the compressed air is used as a so-called carrier.
In the oil-air lubricating method like this, an oil-air lubricating device and a mixing valve, as well as a compressor and external piping are necessary externally of the spindle or the like in which the bearing, which is an object for lubrication, is incorporated, and in addition to this, passageways for oil and air need to be formed in an interior of the spindle or the like. This causes problems that the production costs are increased and that the noise level is increased due to the use of compressed air.
With a view to solving the problems, there has been proposed a rolling bearing device in which a lubricating oil supply mechanism installed in an interior of a rolling bearing (refer, for example, to Patent Document No. 1).
In this proposed technique, a tank for storing lubricating oil and a pump are mounted on a stationary ring side of the rolling bearing, and a nozzle is mounted on the pump in such a manner as to extend to open in the immediate vicinity of a rolling element which rolls between inner and outer rings of the rolling bearing, so that an extremely minute amount or, for example, several tens of nl (or several tens of μcc) of lubricating oil is dropped down towards the rolling elements which rotationally pass thereunder. By this configuration, since the lubricating oil is supplied to the inside of the air curtain which is formed when the rolling bearing rotates, compressed air such as that functioning as the carrier in the oil-air lubricating method becomes unnecessary, so as to solve the problem of noise, and moreover, the compressor and the oil-air lubricating device, as well as the external piping and internal piping also become unnecessary, in which the technique in Patent Document No. 1 becomes advantageous.
In the rolling bearing device with this type of lubricating function, how to cause the lubricating oil supplied from the nozzle to efficiently contribute to lubrication between the rolling elements and the bearing rings constitutes a crucial problem to be solved. Since the rotary rings, rolling elements and a cage of the rolling bearing rotate at high speed, there sometimes occur a case where the lubricating oil so supplied to adhere to any of the constituent elements of the rolling bearing is subject to force acting in a direction going away from the rotational center of the rotating constituent elements (hereinafter, referred to as centrifugal force) to thereby be made difficult to flow between the bearing rings and the rolling elements. When taking the centrifugal force like this into consideration, a preferred arrangement of the nozzle is represented by a nozzle position illustrated in a sectional view of a rolling bearing device shown in FIG. 9 which is taken along parallel to the axis thereof. In an example of a rolling bearing device shown in FIG. 9, a configuration is adopted in which a tank (not shown) for storing therein lubricating oil and an oil supply unit, which is made up of a pump 66 for sucking out the lubricating oil stored in the tank for discharge, a nozzle 67 mounted at a discharge port of the pump 66 in such a manner as to extend between an inner circumferential surface of the cage 64 and an outer circumferential surface of the inner ring 61 and to be made open at a distal end thereof and a drive unit (not shown) for driving the pump 66, are fixed to the immediate vicinity of a rolling bearing which is made up mainly of an inner ring 61, an outer ring 62, rolling elements 63 and a cage 64, or to a spacer 65 which is disposed adjacent to the outer ring 62 which constitutes a stationary ring of the bearing.
According to the arrangement of the nozzle 67 like this, lubricating oil supplied from the distal opening of the nozzle 67 on to the inner circumferential surface of the cage is caused to move over the rolling elements 63 towards a raceway surface of the outer ring 62 and to be transferred to adhere to a raceway surface of the inner ring 61 via the rolling elements 63 by virtue of the centrifugal force generated by virtue of the rotation of the rolling bearing, thereby making it possible to lubricate the rolling bearing effectively.
Incidentally, in addition to the centrifugal force, force due to an airflow generated in the interior of the rolling bearing by virtue of the rotation of the bearing is also caused to act on the lubricating oil supplied from the nozzle which is made to open to the interior of the rolling bearing. Therefore, even in the event that a nozzle arrangement as shown in FIG. 9 is adopted so as to supply almost all the lubricating oil so supplied on to the inner circumferential surface of the retainer 64, there sometimes occurs a case where the lubricating oil is caused to flow on the inner circumferential surface of the cage 64 towards an opposite side to the rolling element 63 as indicated by an arrow shown in FIG. 9 to thereby flow out of the rolling bearing due to disturbance in the airflow in the interior of the bearing, and hence, it cannot be assured that the whole amount of lubricating oil supplied contributes to the lubrication of the bearing.
Conventionally, methods of jet lubrication, oil mist lubrication, oil-air lubrication and the like are known as methods for supplying lubricating oil into an annular space defined in a rolling bearing which is rotating at high speed.
In these methods, however, in order to cause lubricating oil to reach the inside of the annular space from the outside thereof, the lubricating oil needs to be pressurized or accelerated by compressed air, which results in large-scale appurtenant equipment including a compressor and the like. In addition, since an amount of lubricating oil that is more than required is supplied, a large amount of lubricating oil is eventually wasted. In order to prevent environmental pollution, a mechanism for recovering and circulating excess lubricating oil has been required.
To cope with this issue, as a method for supplying uniformly and securely a minute amount of lubricating oil to a plurality of bearings in a stable fashion from a single lubricating device without using a compressor, there has been proposed a lubricating device including nozzles for discharging lubricating oil to the bearings, oil lubricating pumps for supplying lubricating oil to the nozzles and a multi-distribution mechanism for distributing a minute amount of lubricating oil to each of the pumps (refer, for example, to Patent Document No. 2).
In addition, the inventor of the present application and others have also proposed compact rolling bearing devices in which a pump, a tank and an oil supply unit which includes a battery or a generator as a power supply are provided in an annular space of a rolling bearing (refer to Patent Document Nos. 1, 3 and the like).    Patent Document No. 1: JP-A-2004-108388    Patent Document No. 2: JP-A-2002-130589    Patent Document No. 3: JP-A-2004-316707
Incidentally, in the rolling bearing devices which adopt the conventional oil-air lubrication, oil mist lubrication or the lubricating mechanism disclosed in Patent Document No. 1 above, divided housings each having lubricating oil supply holes which are distributed in an equal number, a multi-distribution mechanism which is made up of a distributor or a rotary valve for distributing lubricating oil equally to each piping and a motor, and the like are necessary, and this still requires the complex configuration to remain around the bearing, thereby making it difficult to make the rolling bearing device small in size and reduce the production costs thereof. In particular, in the event that the piping is long which extends from the pump to the nozzle for supplying lubricating oil, the pulsation (pressure) of lubricating oil which is generated by the pump is attenuated, leading to a fear that a required lubricating oil discharging speed or lubricating oil discharge amount at the distal end of the nozzle cannot be obtained.
In addition, when the oil supply unit which includes the pump, the tank, and the battery or the power source are provided in the annular space of the rolling bearing, the configuration around the bearing becomes simple. However, the capacity of the tank is limited due to the power supply being so provided, whereby a period of time during which lubricating oil can be supplied becomes relatively short, and the costs are increased. In particular, in the event that the oil supply unit is not provided with a sensor for detecting peripheral conditions, since the rotational state of the bearing cannot be detected, when the rolling bearing does not rotate, the oil supply unit has to manually be stopped so as to prevent a continued wasteful supply of lubricating oil.
Furthermore, in a case where the rolling bearing with the oil supply unit is incorporated in the housing, it becomes difficult to manually stop the oil supply unit, or even though the oil supply unit can be stopped manually, there is caused a fear that a leakage of lubricating oil occurs due to heat being generated on the periphery of the bearing immediately after the rotation of the bearing is stopped.
In addition, in a case where the plurality of rolling bearings are provided, it is difficult to stop the rolling bearings altogether at one time, and the discharge of lubricating oil cannot be stopped at a suitable timing for the stop of rotation of the bearings. Because of this, there is caused a possibility that excess lubricating oil is discharged into the annular spaces in the bearings.